Electronic switches with high "off" impedance and virtually zero "on" impedance are desirable in many applications. For example, in knock sensor signal conditioner systems for internal combustion engines such an electronic switch with low dynamic "on" resistance is desirable to switch resistors used to select the center frequency of the knock signal being sensed.
Presently, MOSFET switches, or inverted mode bipolar chopper transistors, are often used as low resistance electronic switches, but the currently available devices, in order to provide a very low (less than an ohm) dynamic impedance, are of such a large size that they are impractical for many applications. As the available parameters concerning size constraints, parts, devices and material selection narrow in a given design, the use of MOSFET type switches becomes increasingly outmoded. That is the case with such switches needed for switching the bandpass selection resistors in knock sensor signal conditioner systems which form a part of knock sensor units in the electronic control circuits used with internal combustion engines. Electronic control circuits are used with internal combustion engines in order to optimize their operation under a variety of conditions. One component of such control circuits is "knock" sensor units which sense "knocking" or pre-ignition during engine operation and adjust various parameters such as timing and fuel mixture in order to minimize knocking. Knocking can be caused by a variety of factors including timing, fuel mixture, compression ratio, manifold pressure, exhaust back pressure, and fuel octane rating. Knocking is undesirable because it increases wear and decreases efficiency. A knock sensor unit uses one or more sensors to sense the vibrations caused by the knocking. The detecting of knocking is used to generate a signal which is used by the controller circuit to adjust various engine parameters and reduce or eliminate the knocking.